wikimedia/mediawiki-extensions-Translate

$( function () {
    var appendFromSelect = function ( selectid, targetid ) {
        'use strict';

        var select = document.getElementById( selectid ),
            target = document.getElementById( targetid );

        if ( !target || !select ) {
            return;
        }

        var atxt = select.options[ select.selectedIndex ].value;

        if ( !atxt ) {
            return;
        }

        if ( target.value.replace( /\s+/g, '' ) !== '' ) {
            atxt = ', ' + atxt;
        }

        atxt = target.value + atxt;

        atxt = atxt.replace( /\bdefault\b[,\s]*/i, '' );

        target.value = atxt;
    };

    $( '.mw-translate-jssti' ).on( 'click', function () {
        var sourceId = $( this ).data( 'translate-jssti-sourceid' ),
            targetId = $( this ).data( 'translate-jssti-targetid' );

        appendFromSelect( sourceId, targetId );
    } );

} );